This invention is based on and claims priority to Japanese Patent Applications No. Hei 11-277911, filed Sep. 30, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to an engine for a watercraft, and more particularly to an arrangement of an air induction system of an engine most suitable for a personal watercraft.
2. Description of Related Art
Personal watercrafts have become very popular in recent years. This type of watercraft is quite sporting in nature and caries one or more riders. A relatively small hull of the personal watercraft commonly defines a rider""s area above an engine compartment. An internal combustion engine powers a jet propulsion unit which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on an underside of the hull. The jet propulsion unit, which includes an impeller, is placed within the tunnel. The impeller has an impeller shaft driven by the engine. The impeller shaft usually extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.
The engine includes an air induction system for introducing air into one or more combustion chambers. The air induction system includes one or more throttle bodies associated with the combustion chambers. Each throttle body has a throttle valve admitting air into the combustion chambers. Typical throttle bodies are made of metal material. This metal material, however, is likely to be corroded by water, particularly, by salt water. Because the engine for the watercraft often is exposed to water, water protection of engine components is a concern.
A need therefore exists for an improved engine that can protect a throttle body or throttle bodies from water so as to preclude the throttle bodies from corrosion.
In addition, although personal watercraft with a four-cycle engine are now being designed primarily for reducing exhaust emissions. The four-cycle engine normally needs a plenum chamber that has a relatively large volume so as to obtain high performance under all running conditions. The four-cycle engine, however, has two or more valves and a valve drive mechanism arranged to activate the valves. Such a large plenum chamber, multiple valves and a valve drive mechanism, as well as the foregoing throttle bodies, are thus factors that make the engine larger in height and/or in width. On the other hand, because the rider""s area is defined above the engine compartment as noted above, the capacity and height of the engine compartment is extremely limited. Otherwise, the seat position must be higher and/or wider and this is not comfortable for the rider.
Another need therefore exists for an improved engine, particularly, an improved four-cycle engine but not limited thereto, that can have a relatively large plenum chamber notwithstanding having a number of engine components greater than a two-cycle engine and notwithstanding being placed in a relatively narrow engine compartment.
In accordance with one aspect of the present invention, an internal combustion engine is provided for a watercraft that has a hull defining an engine compartment in which the engine is placed. The engine comprises a cylinder block defining at least one cylinder bore. A piston reciprocates within the cylinder bore. A cylinder head member closes an end of the cylinder bore and defines a combustion chamber with the cylinder bore and the piston. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes a plenum chamber member defining a plenum chamber. The plenum chamber member has an air inlet port for the plenum chamber. A throttle body has a throttle valve admitting air to the combustion chamber from the plenum chamber. The throttle body is disposed within the plenum chamber.
In accordance with another aspect of the present invention, a watercraft comprises a hull defining an engine compartment and a rider""s area above the engine compartment. An internal combustion engine is disposed within the engine compartment. The engine includes an engine body in which a combustion chamber is defined. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes a plenum chamber member and a throttle body. The plenum chamber member defines a plenum chamber and has an air inlet port. The throttle body has a throttle valve admitting air to the combustion chamber from the plenum chamber. The throttle body is positioned within the plenum chamber.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.